In a non-pendulum car disclosure, U.S. Pat. No. 4,754,849, Hiroshi Ando shows electromagnets disposed outside the car symmetrically about guide rails in a control system using opposing forces from the electromagnets to keep the car steady using the rails as the necessary ferromagnetic mass but, rather than using the rails as a straight reference line, instead using a cable stretched between the top and bottom of the hoistway. The position of the car with respect to the cable is controlled using detectors in a closed loop control system. There is serious question as to whether such a cable can be successfully used as a reliable guide of straightness. Moreover, the Ando disclosure requires the use of twelve electromagnets with separate control and power circuits. Furthermore, the use of guide rails such as are disclosed by Ando will require fairly massive coils in order to generate the large amount of flux density required, given the (i) not insignificant force required to move the weight of the elevator cab, (ii) the necessarily small utilizable surface area on the rail, and (iii) the relatively large airgap required as compared to the rail thickness.
In another non-pendulum car disclosure, U.S. Pat. No. 4,750,590, Matti Otala discloses what appears to be an essentially open loop control system with solenoid actuated guide shoes that uses the concept of memorizing the out-of-straightness of the guide rails for storage in a computer memory and then sensing the position of the car in the hoistway for the purpose of recalling the corresponding information from memory and correcting the guide rail shoe positions accordingly. An acceleration sensor is mentioned in claim 6 but does not appear to be otherwise disclosed as to its purpose in the specification or drawing. Perhaps it is used to determine the acceleration of the car in the hoistway. Such an acceleration signal would presumably be needed to determine which data point to retrieve from memory as suggested in claim 2. Otala's approach suffers from the problem of changes in the out-of-straightness before a correction run can be effected and the accuracy with which the stored information can be made to conform to the car's actual position.
A mounting arrangement for a pendulum or hung car is shown in U.S. Pat. No. 4,113,064 by Shigeta et al wherein the cab is suspended within and from the top of an outer framework by a plurality of rods connected to the bottom of the cab. A plurality of stabilizing stoppers are shown interposed between the underside of the hung cab and the floor of the frame. Each stopper comprises a cylinder extending downward from the underside of the hung cab surrounding a rubber torus placed on an upright rod extending from the floor of the frame. Clearance between the cylinder and the cab is sufficient to permit movement but insufficient to allow the cab to strike the frame. Another embodiment comprising bolster means having ball bearings permits movement in any direction of the horizontal plane.
Another approach is disclosed by Luinstra et al in U.S. Pat. No. 4,660,682 wherein a pair of parallel rails are arranged horizontally in a parallelogram between the suspended cab and frame with followers farranged to roll or slide on the rails in such a way that the cab can move in any horizontal direction relative to the frame.
Both of the last two pendulum car approaches employ passive restraints on movement which by nature are reactive rather than active.